• Diameter: 4 in
• Housing: Aluminum
• Housing Finish: Hard Anodized
• Seals: Neoprene
• Standard Cracking Pressure: 1.00 ± 20% inches of water

Drawing   3D Model

The 556 two-way pressure relief valve is used extensively on military enclosures and provides pressure relief in a variety of scenarios. It protects the enclosure from excess pressure and vacuum during air transport, equalizes pressure due to temperature fluctuations, and relieves back pressure developed when a door is opened and closed.

The 556 can be configured with many pressure settings and with a sealed cover or louvered cover. The most common configurations are shown below.